Long strings of tubular pipe sections (“tubulars”) are typically used in the operation of offshore oil and gas wells. These strings are used to drill deep into the earth, in the case of a drill string; to connect the wellhead on the ocean floor to the surface platform and isolate the drill string from the ocean water, in the case of a riser string; to line the wellbore, in the case of a casing string; and to deliver the oil or gas produced from the well to the platform, in the case of a production tube string. These strings can be hundreds or thousands of feet long and made up of hundreds of tubulars joined together, so the process of coupling and decoupling these various tubulars is central to the operation of an offshore well. Land-based wells similarly utilize long tubular strings.
The coupling of tubulars generally occurs by the alternating use of a crane that lowers or supports (an “elevator”) and a mechanism through which the tubular string passes that grips and supports the string (a “tubing spider”). As the tubing spider grips and supports the tubular string, the elevator lifts a new length of tubular into alignment with the existing string. Once the new length of tubular is in alignment with the string, the elevator lowers the tubular for coupling to the string and a connection is formed. The elevator, still attached to the tubular, then lifts the entire tubular string to take the weight off the spider, and the spider disengages to release the string. Finally, the elevator lowers the string through the spider by the length of one tubular and the spider once again engages to grip and support the string and the process repeats for as many lengths of tubular as are necessary. Decoupling of the tubular string occurs by the same general process.
Each of the steps of coupling or decoupling a tubular string is traditionally performed by platform workers, often by hand. As a result, the workers may be in close proximity to high pressure fluids and heavy equipment such as the spider, the elevator, and other machinery. This results in a risk of injury to the workers, of damage to the equipment, and of costly production downtime from even minor mistakes. Tubular strings may be customarily “retrieved” and “run” (i.e., entirely dismantled and reassembled) multiple times per year, so these risks can recur throughout the life of a producing well.
Consequently, there is a need for a spider control system that automatically performs the handling, coupling, and decoupling of tubulars without the need for local or remote human input or control.